Waveguide polarizer

ABSTRACT

The waveguide polarizer is a device for microwave antenna systems consisting of a waveguide section, with circular cross-section, being equipped with two terminal flanges for connection to other circular guides. A certain number of elliptical irises are arranged inside at regular intervals, resting on parallel planes and all oriented in the same way, i.e. with their longer axes all belonging to the same axial plane.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/IT01/00063 filed 13 Feb.2001 and is based upon Italian national application TO 2000 A 000192filed 29 Feb. 2000 under the International Convention.

TECHNICAL FIELD

This invention relates to devices for telecommunication systemsemploying microwaves and, in particular, it relates to a waveguidepolarizer.

BACKGROUND ART

As known, a polarizer is a device for microwave antenna systems, madewithin a waveguide structure, capable of transforming thecharacteristics of an electromagnetic field that propagates inside thepolarizer. Particularly, the polarizer can transform a linear polarizedelectromagnetic field into a circular polarized electromagnetic fieldand vice versa, being reciprocal in its operation.

As is known, there are two main groups of polarizers, according to thetype of inserts arranged inside the waveguide to generate the necessaryshifting of the orthogonal components of the electromagnetic field. Asdescribed in the book entitled “Waveguide Components for Antenna FeedSystems: Theory and CAD” written by J. Uher et al., 1993 Artech House,these inserts can be of the septum or iris type.

A septum polarizer may consist of a waveguide section, with squarecross-section, inside which a metal stepped septum is arranged inparallel to the sides and in an intermediate position. Operation isbased on the transformation of the square cross-section guide into tworectangular cross-section guides, in which the polarized fields arepropagated orthogonally.

An iris polarizer may consist of a waveguide section, is with circularcross-section, inside which the irises, consisting of two equal andcounterpoised circular segments, are arranged in the form of a cascade.The irises may have different dimensions, but are generally arranged atregular intervals. Their purpose is to vary the transverse dimensions ofthe guide so as to generate different phase shifts between theorthogonal components of the electromagnetic field. The global shiftingis achieved by summing the partial shifting introduced by each iris. Asimilar polarizer can also be made by implementing a square waveguide byusing rectangular shape irises.

To construct an iris polarizer, the waveguide is made of twolongitudinal halves, equipped with suitable flanges, to allow the twohalves to be screwed together. Inside each half, the irises are made bymeans of a suitable form of mechanical machining, generally by means ofmilling and electro-etching.

During assembly, special care is required to exert the right tighteningpressure on the screws, to avoid undesired deformation of the guide,with consequent errors in the amount of shift introduced.

In order to prevent such a problem, the guide should be, a single piece,but this would cause greater problems for the mechanical machining ofirises. This is because the irises would need to be made usingspecifically constructed electro-etching tools which would have to beused in conditions with no visibility and which will produce the sharpedges between each iris and the inner side of the guide.

Another requirement is to make the polarizer according to an accurate todesign, which will result in operation that is compliant with therequired specifications, thus avoiding the need to conduct adjustmentsand calibrations after the device has been completed.

The design may be accurate if the mechanical characteristics of thepolarizer, and consequently, of the guide with the respective irises,can be expressed by means of a very accurate and efficientelectromagnetic model. The automated procedures which are currentlyavailable allow this, providing that the transverse sections of thepolarizer, corresponding to both the irises and the envelope, can berepresented by means of simple geometrical shape uch as squares,rectangles, circles and ellipses.

SUMMARY OF THE INVENTION

The waveguide polarizer described herein avoids these problems allowing:

an automated design procedure, thankes to accurate and efficientelectromagnetic modeling of mechanical characteristics;

simplified mechanical construction in a single piece;

use of milling alone to make the irises, since machining the edges ofthe transverse sections is not required; and

connection to other circular guides, of the type commonly used inantenna feeders, without the need of rectangular-to-circular waveguidetransition pieces.

Particularly, this invention relates to a waveguide polarizer comprisedof a waveguide section, with circular cross-section, inside which acertain number of elliptical irises are arranged at regular intervals,lying in parallel planes and all oriented in the same way, i.e. withtheir longer axes all belonging to the same axial plane.

BRIEF DESCRIPTION OF DRAWINGS

This characteristic, and others, of this invention will be illustratedwith reference to a preferred embodiment, as non-limiting examples, inthe enclosed drawings, wherein:

FIG. 1 is a longitudinal cross-section of the waveguide polarizer;

FIG. 2 is an end view; and

FIG. 3 is a perspective view.

BEST MODE FOR CARRYING OUT THE INVENTION

As shown in the figures, the polarizer consists of a circularcross-section waveguide section 1 equipped with two terminal flanges 2for connection to other circular guides, and a certain number ofelliptical irises 11, 12 and 13. The irises are arranged at regularintervals, lying in parallel planes and all oriented in the same way,i.e. with their longer axes all belonging to the same axial plane.Furthermore, the longer axes are advantageously equal to the internaldiameter of the guide, while the shorter axes are gradually tapered,from the ends to the half-way point of the polarizer, in alongitudinally symmetrical way.

Having established the number of irises according to the passband widthand band ripple, one of the known automated design procedures willprovide the constructive parameters of the polarizer when updatedimplementing the elliptical shape of the irises proposed in thisinvention. Particularly, the distance between the irises and theirthickness (quantities which are normally constant), as well as theshorter axes of the ellipses, will be provided.

Naturally, numerous changes can be made to the construction and forms ofembodiment of the invention herein envisaged, all comprised within thecontext of the claims hereof.

What is claimed is:
 1. A waveguide polarizer comprising: a waveguidesection having circular cross-section; and a plurality of ellipticalirises arranged inside said waveguide section at regular intervals, saidirises lying in respective mutually parallel planes and being orientedwith respective longer axes all in a common axial plane.
 2. Thewaveguide polarizer according to claim 1 wherein the longer axes of saidirises are each equal to an internal diameter of the waveguide.
 3. Thewaveguide polarizer according to claim 2 wherein shorter axes of saidirises are gradually tapered from respective ends to the half-way pointof the polarizer in a longitudinally symmetric way.
 4. The waveguidepolarizer according to claim 2 wherein shorter axes of said irises aregradually tapered from respective ends to the half-way point of thepolarizer in a longitudinally symmetric way.
 5. The waveguide polarizerdefined in claim 1 wherein said section is formed in one piece with saidirises from metal, has flanges at opposite ends thereof, and the longaxes of said irises are all equal to an internal diameter of saidwaveguide section.